Catalysts for the control of coking during steam reforming

Catalytic steam reforming of light hydrocarbons is the major industrial route to the production of hydrogen and synthesis gas. The product spectrum is dictated by thermodynamics, with hydrogen favoured at high temperatures. The formation of coke, also favoured under these conditions, is a major problem. The mechanism of coke formation is reviewed and different approaches to control coking are discussed. Ensemble size control produced by adsorbing controlled amounts of sulphur on the nickel surface has been found to be very effective at controlling coking. An approach based on the prevention of carbide formation has also been shown to be extremely effective, although the exact mechanism of coke minimisation is uncertain. Small amounts of tin reduce coking very significantly. Indications exist that the use of rare earth oxides as supports can also reduce coking. Further study of this finding is recommended. (C) 1999 Elsevier Science B.V. All rights reserved.